//
// This software is now distributed according to
// the Lesser Gnu Public License. Please see
// http://www.gnu.org/copyleft/lesser.txt for
// the details.
// -- Happy Computing!
//
package com.stevesoft.pat;

/**
 * This class allows you to match on a partial string. If the allowOverRun flag
 * is true, then the length() method returns a number 1 larger than is actually
 * contained by the class.
 * <p>
 * If one attempts to access the last character as follows:
 * 
 * <pre>
 *  StringBuffer sb = ...;
 *  ...
 *  PartialBuffer pb = new PartialBuffer(sb);
 *  char c = pb.charAt(pb.length()-1);
 * </pre>
 * 
 * then two things happen. First, a zero is returned into the variable c.
 * Second, the overRun flag is set to "true." Accessing data beyond the end of
 * the buffer is considered an "overRun" of the data.
 * <p>
 * This can be helpful in determining whether more characters are required for a
 * match to occur, as the pseudo-code below illustrates.
 * 
 * <pre>
 *  int i = ...;
 *  Regex r = new Regex(&quot;some pattern&quot;);
 *  pb.allowOverRun = true;
 *  pb.overRun = true;
 *  boolean result = r.matchAt(pb,i);
 *  if(pb.overRun) {
 *  // The result of the match is not relevant, regardless
 *  // of whether result is true or false.  We need to
 *  // append more data to the buffer and try again.
 *  ....
 *  sb.append(more data);
 *  }
 * </pre>
 */
class PartialBuffer implements StringLike {

	int off;
	public boolean allowOverRun = true;
	public boolean overRun = false;
	StringBuffer sb;

	PartialBuffer(StringBuffer sb) {
		this.sb = sb;
	}

	public char charAt(int n) {
		n += off;
		if (n == sb.length()) {
			overRun = true;
			return 0;
		}
		return sb.charAt(n);
	}

	public int length() {
		return allowOverRun ? sb.length() + 1 : sb.length();
	}

	public int indexOf(char c) {
		for (int i = 0; i < sb.length(); i++)
			if (sb.charAt(i) == c)
				return i;
		return -1;
	}

	public Object unwrap() {
		return sb;
	}

	public String substring(int i1, int i2) {
		StringBuffer sb = new StringBuffer(i2 - i1);
		for (int i = i1; i < i2; i++)
			sb.append(charAt(i));
		return sb.toString();
	}

	/** Just returns null. */
	public BasicStringBufferLike newStringBufferLike() {
		return null;
	}
}
